Fibrous sheet materials, particularly fibrous sheet materials for absorbing fluids, are manufactured for many uses, for example they are incorporated into absorbent articles such as disposable diapers, incontinent pads and catarnenial napkins as fluid absorption or fluid transmission and/or diffusion elements, for example, as absorbent cores that are intended to absorb and retain body fluids. Fibrous sheet materials, and more specifically fibrous sheet materials used to absorbem articles as fluid absorption or fluid transmission and/or diffusion elements, usually comprise a multiplicity of components so as to improve their specific performances; further components can be also included to provide the structure with added benefits.
Dry laying and, more specifically, air laying processes are widely used to produce webs from dry fibres, which can in turn be used e.g. as sheet materials for absorbing fluids. Particularly, the air laying process refers to the formation of webs with a random fibre orientation; the properties of such air laid webs are therefore somewhat isotropic. The fibrous sheet materials produced by airlaying processes are soft, flexible and porous, and are particularly suitable for use as liquid absorbent structures in absorbent articles, such as disposable diapers, sanitary napkins, pantiliners, incontinent pads, and wipes.
The airlaying manufacturing process generally comprises a web formation and layering step and a web bonding and stabilizing step; in airlaying processes in fact the fibres, that can be of any type, e.g. cellulosic, synthetic, or any combination thereof, are formed or condensed into a web, but such web lacks integrity, and mast, therefore be stabilized. Different techniques for bonding and stabilizing a dry formed web are known in the art, i.e. mechanical, thermal and chemical bonding processes. Bonding a web structure by means of a chemical is one of the most common methods of bonding in the nonwoven industry, and consists in the application of a chemical binder to the web and in the curing of the binder. The most widely used chemical is latex, since it is cheap, versatile, easy to apply, and very effective as a binder. Several methods are known to apply the latex binder to the fibrous web, while spray bonding and print bonding am particularly preferred for fibrous webs intended to be used in absorbent articles.
The latex binder is usually an aqueous emulsion, and can be applied to one or both major flat surfaces of the fibrous web. The desired amount is measured in order to provide the structure with stability and strength, at the same time without impairing fluid handling, typically absorption and/or acquisition capacity. The latex binder in fact while binding the fibres together, also to a certain extent coats them, and can at least partially reduce the capability of the fibrous sheet material of acquiring and absorbing fluids. Also, a selected amount of latex which may be optimal in order to provide the airlaid sheet material with the desired stability and strength may influence negatively its flexibility and softness, actually reducing it.
Hence, there still exists a need for an airlaid sheet material stabilized by means of a latex binder and capable of providing effective fluid handling combined with softness and flexibility, while at the same time also having the desired strength and stability. It has now been discovered feat this need can be addressed by an airlaid sheet material stabilized by means of a latex binder provided in a selected distribution, therefore providing an absorbent structure which is soft and has a good integrity, while also featuring improved fluid handling capability.